This application claims the priority of German application 197 06 066.8 filed in Germany on Feb. 17, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a compressor for generating compressed air in motor vehicles, with a drive driven by a drive shaft, provided with a swash plate and lubricated by oil, said drive being connected by piston rods with pistons traveling in cylinder bores.
One-cylinder or two-cylinder compressors are used everywhere today for generating compressed air in motor vehicles. The compressors are mounted on the engines of the vehicles and are driven directly off the engine through gears, and in some cases by V-belts as well. The compressors are lubricated by the oil circuits of the engines. As a result, oil also necessarily enters the compressed air through the compressor pistons. Depending on the condition of the compressors, these quantities of oil can be considerable and for the most part they enter the environment at the ventilation openings of the compressed air systems, usually onto the road, and hence can be viewed as an environmental hazard. With the high operating pressures conventionally used today and the high thermal stress associated therewith, a portion of this oil is also coked in the compressor; the oil coke settles out in the cylinder head of the compressor and in the devices connected downstream, where it has a highly deleterious effect on service life.
These compressors are regulated by pressure regulator valves (governors). The air stream delivered by the constantly driven compressor is throttled by a device on the compressor during the idle phase or vented into the atmosphere by vent devices on the pressure-regulating valves. The energy consumed by the compressor during this idle phase amounts to pure lost energy. The share of this lost energy within the total energy consumption of the compressor is not insignificant because the effective ON time ED, in other words the time during which the compressor is delivering compressed air to the system, rarely comprises more than 30% of the entire operating time of a vehicle. The compressor is not shut down by means of a shutoff clutch for example because the torque curve, especially the torque peaks, makes very large and expensive clutches necessary.
Another disadvantage consists of the negative torque components after the top dead center (TDC) point of the piston in the compressor. These components in a gear drive result in flank alternation in the gears and hence to a considerable noise impact. In vehicles in which this is not desirable, expensive measures applied to the gears (minimization of flank play, gears pretensioned tangentially) are employed to solve this problem more or less satisfactorily.
Hence, a goal of the invention is to design a compressor that is used especially for generating compressed air in motor vehicles, said compressor not suffering from the above disadvantages and problems and, with its compact design, nevertheless being possible to manufacture economically by comparison with compressors of current design.
This goal is achieved according to preferred embodiments of the invention by providing a compressor for generating compressed air in motor vehicles, with a drive driven by a drive shaft, provided with a swash plate and lubricated by oil, said drive being connected by piston rods with pistons traveling in cylinder bores, wherein the oil-lubricated drive of the compressor is sealed off from oil-free chambers located on backs of respective ones of the pistons by sealing elements acting relative to each of the piston rods, wherein the oil free chambers are connected with one another by an annular chamber and are linked to a common intake connection, and wherein each piston has an intake valve such that pressure chambers of the compressor are formed between the front of the respective piston and the cylinder head.
The compressors according to the invention are characterized by largely oil-free operation since the wiping and sealing elements acting on the piston rods create a very effective seal between the drive and compressor parts, in other words, with respect to the intake chamber located on the back of the piston.
In this way, it is possible to mount the intake valves on the piston, in other words the compressor draws in air through the pistons. This also has the advantage that more room is available for cooling in the cylinder head, so that in many cases it is possible to cool the compressor with cooling oil from the lubricant circuit of the vehicle. However, this does not rule out the use of water cooling for the compressor under higher thermal stress.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.